The present invention relates to a developer used for making lithographic printing plates by silver complex diffusion transfer process.
Printing plates which use silver images obtained by silver complex diffusion transfer process (DTR process) which is one of photographic reproduction methods as offset printing master plates are disclosed in U.S. Pat. No. 3,857,112.
According to a typical silver complex diffusion transfer process suitable for making these lithographic printing plates, a light-sensitive material which comprises a support and a subbing layer which serves also as an antihalation layer, a silver halide emulsion layer and a physical development nuclei layer provided on said support is exposed imagewise and developed, whereby silver halide of latent image area becomes black silver by chemical development in the emulsion layer and simultaneously silver halide of non-latent image area is dissolved by the action of a silver halide complexing agent contained in a processing solution and diffuses to the surface of the light-sensitive material. The thus dissolved and diffusing silver complex salt is deposited on the physical development nuclei in the surface layer by reducing action of developing agent. Following the development, if necessary, the material is subjected to sensitizing treatment to increase ink-receptivity of the silver image. Then, the thus obtained lithographic printing plate is mounted on an offset printing machine and the inked image is transferred to a printing paper.
Various properties required for the printing plates depend on printing materials and besides, depend greatly on plate making steps, especially development processing step. That is, the influence of properties of silver image produced by diffusion transfer on printing characteristics is important. For example, conditions for formation of transfer silver grains such as diffusion rate, stability and reducing rate of silver complex salt are important factors. Furthermore, U.S. Pat. Nos. 4,297,429, 4,297,403 and 4,355,090 show that kind of silver halide solvents has an important influence on the conditions for formation of transfer silver grains. However, there have been found few silver complexing agents which are fully satisfactory.